Dynamic Energy Budget Theory - I
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Transcript of Dynamic Energy Budget Theory - I
Dynamic Energy Budget Theory - I
Tânia Sousa with contributions from : Tjalling Yager & Bas Kooijman
Toxicology
Which is the toxicity of the environmental concentration of a compound?
Which are the toxic effects of a compound?
Climate Change Will an increase in 1ºC have a
drastic impact on the distribution range of a species?
Waste water treatment plant What are the necessary conditions
to mantain an healthy microbian comunity in the biological reactors?
Environmental Applications
Human-made toxicants
Wide variety of uses paints, detergents, solvents, pesticides,
pharmaceuticals, polymers, … probably some 100.000 compounds
Chemical industry is BIG business! production value 2009: 3.4 trillion
dollar (3.400.000.000.000 $) equals the GDP of Germany
All are toxic, some are intended to kill fungicides, insecticides, herbicides,
nematicides, molluscicides, …
Human-made & natural toxicant
Dioxins e.g., 2,3,7,8-TCDD human: paper and fiber bleaching, incineration
of waste, metal smelting, cigarette smoke natural: incomplete combustion of chlorine-
containing things
Human-made vs. natural
What is the difference? Time scale
major increase after second world war rapid development of new types of molecules
Spatial scale amounts emitted landscape and even global instead of local
Since 1970’s, most countries have programmes for environmental protection ...
Daphnia reproduction test OECD guideline 211
Ecotoxicology
Reproduction test
Reproduction test
Reproduction test
wait for 21 days …
Range of Concentrations
Dose-response plot
EC50
tota
l off
spri
ng
log concentration
NOEC
If EC50 is the answer …… what was the question?“What is the concentration of chemical X that
leads to 50% effect on the total number of offspring of Daphnia magna (Straus) after 21-day constant exposure under standardised laboratory conditions?”
What does this answer tell me about other situations? (almost) nothing! EC50EC50
tota
loffs
prin
g
log concentration
Organisms are complex…
Response to stress depends on organism (species, life stage, sex, …) endpoint (size, reproduction, development, …) type of stressor (toxicant, radiation, parasites,
…) exposure scenario (pulsed, multiple stress, …) environmental conditions (temperature, food,
…) etc., etc.
E.g., effect on reproduction
E.g., effect on reproduction
E.g., effect on reproduction
E.g., effect on reproduction
E.g., effect on reproduction
To understand an effect on reproduction …• need to know how food is used to make offspring• and how chemicals interfere with this process
Why is DEB important for
toxicity? The use of DEB theory allows extrapolation of
toxicity test results to other situations and other species
To study the effects of toxicity on life-history traits, DEB follows naturally food is used to fuel all traits over the life cycle toxicants affect DEB parameters should allow extrapolation to untested
conditions it is valuable for environmental risk assessment
It captures the quantitative aspects of
metabolism at the individual level for all species
Why the hope for generality? universality of physics and evolution
Entropy production is >=0 widespread biological empirical patterns
What is DEB theory?
A widespread biological empirical
fact: Von Bertalanffy growth
trb
BeLLLtL )()(
Growth as a function of time
Depends on length at birth, maximum length and growth rate
It was proposed in 1938 by Von Bertalanffy an austrian biologist
Consistency with other scientific knowledge
(thermodynamics, evolution, etc) Consistency with empirical data Life-cycle approach: embryo, juvenile and
adult
Occam’s razor: the general model should be as simple as possible (and not more)
Basic concepts in DEB Theory
Metabolism in a DEB
individual. The boundary of the
organism Rectangles are state
variables
A DEB organism
ME - Reserve
MV - StructureMH - Maturity
What defines a DEB organism?
Biomass Mv - Mass of Reserve ME - Mass of Structure
Life-Cycle approach: different life stages MH - Level of Maturity (it represents neither mass
nor energy)
What about other possibles state variables such as age?
DEB model: the State Variables
These gouramis are from the same nest, they have the same age and lived in the same tankSocial interaction during feeding caused the huge size differenceAge-based models for growth are bound to fail; growth depends on food intake
Not age, but size Trichopsis vittatus
Strong homeostasis
Reserve & Structure have constant aggregated chemical composition
Weak homeostasis At constant food organisms tend to constant
aggregated chemical composition
DEB model: Reserve and Structure
Why more than 1 state variable to define the biomass? The aggregated chemical composition of organisms is not constant
– it changes with the growth rate Why not use thousands of chemical species to define the
organism? Two are sufficient (in animals and bacteria) to capture the change
in aggregated chemical composition with the growth rate Strong & Weak homeostasis -> higher control over metabolism
Life Stages (dark blue) and transitions (light
blue)
Essential switch points for metabolic behavior Birth (start of feeding) Puberty (start of allocation to reproduction)
Switch points sometimes in reversed order (aphids)
DEB model: Maturity
embryo juvenile adult
fertilization birth puberty deathweaning
baby infant
MHb- threshold of maturity at birth
MHp- threshold of maturity at puberty
Notation 1
Indices for compounds
Indices for transformations
General
Notation 2
Metabolism in a DEB
individual. Rectangles are state
variables Arrows are flows of food
JXA, reserve JEA, JEC, JEM, JET , JEG, JER, JEJ or structure JVG.
Circles are processes
A DEB organism
ME - Reserve
MV - Structure
Feeding
MH - Maturity
XAJ EAJ
Assimilation
Feeding: the uptake of food Assimilation: conversion of substrate (food,
nutrients, light) into reserve(s) Depends on substrate availability & structural
surface area (e.g. surface area of the gut)
Feeding & Assimilation
Empirical pattern: the heat increment of feeding suggests that there are processes only associated with food processing
Strong homeostasis imposes a fixed conversion efficiency Consistency with other fields: mass transfer is proportional to area
- surface maximum assimilation rate -yield of reserve on food
Intra-taxon predation: efficient conversion
yEX a high yield of reserve on food
Hemiphractus fasciatusis a frog-eating frog
Beroe spis a comb jelly-eating comb jelly
Solaster papposus is a starfish-eating starfish
Chrysaora hysoscella is a jelly fish-eating jelly fish
Euspira catena is a snail-eating snail
Coluber constrictor is a snake-eating snake
Asplanchna girodiis a rotifer-eating rotifer
Didinium nasutumis a ciliate-eating ciliate
Esox lucius is a fish-eating fish
Enallagma carunculatum is a insect-eating insect
Falco peregrinus is a bird-eating bird
Acinonyx jubatus is a mammal-eating mammal
Intra-taxon predation: efficient conversionyEX a high yield of reserve on food